Rule: The present tense normally expresses present time reference; the past tense normally expresses past time reference.
Examples of errors:
In most cases the choice between the present or past tense would seem to be a simple one--a straightforward application of Rule 2.2.1. Certainly no one would question the time reference when one refers to one's date of birth, for example, and the problem in a sentence like (9) is not whether the verb should be past or present but simply that the past tense is formed differently in German (Ich bin geboren) than in English. In some cases, though, the question of present or past time reference is not so simple, In (6) reference is made to examples given in the course of the same essay; strictly speaking, the citation of the examples occurred previous to the writing of this sentence, so one might think the past tense is justified. Similarly, (7) refers to "recent" statistics, which obviously were collected and published sometime in the past. Nevertheless, the simple present is preferable in both of these sentences, because the focus of interest is not the past event (i.e. when the examples or statistics were produced) but the present state--the fact that now these examples and statistics reveal certain facts. In (7) the present perfect, showing present results of a past event, is also acceptable.
(8) is also problematic. We can assume from the context that just here is a time adverbial (i.e. does not mean 'only'), but as such it is still ambiguous, since it can mean either 'at this very moment' or 'a moment ago':
He's just coming through the door (i.e. at this very, moment)
He just left (i.e. a moment ago)
The first reading of just almost demands a progressive verb, since it expresses an event or activity in progress, and therefore it is not likely to be found in combination with verbs like remember that do not normally take the progressive. This restriction does not apply to sich errinern, of course, since German has no progressive:
Ich erinnere mich gerade, daß er einen Schnurbart hat.
A further source of confusion is the use of occur, whose meaning is similar to that of remember, and which does allow the construction attempted in (8), in sentences like
It just occurs to me that he has a moustache.
In general, though, just meaning 'at this very moment' must be combined with a verb in the progressive.
As an event verb, remember allows the present progressive in an iterative sense, or in the sense of la mental activity in progress:
He's always remembering scenes from his childhood (iterative)
What are you thinking about? (mental activity)
Oh, I'm just remembering something that happened last week (mental activity)
The second usage is relatively rare, however, and is not appropriate in (8), where the focus of interest is not on the remembering per se (the mental activity) but on what is (or has just been) remembered. (The present perfect is acceptable here as well.)
(10) and (14) are cleft sentences in which a particular element has been singled out and brought forward for prominence. In such sentences the tense in the main clause normally corresponds to the tense in the subordinate clause:
They married 50 years ago.
>It is/*was 50 years ago that they married.
I saw my brother last about a week back.
> It *is/was about a week back that I saw my brother last.
You're the fool!
> It is/*was you who are the fool!
Napoleon lost at Waterloo.
> It *is/was Napoleon who lost at Waterloo.
There is a lot of dialect variation here, though; for example, in Irish English, where cleft sentences are especially common, (10) and (14) would both be acceptable.